Radiation Environment for the LRO
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Robotic Lunar Exploration Program
Lunar Reconnaissance Orbiter (LRO)
Radiation Environment for the LRO
1/26/2005
Goddard Space Flight Center
Greenbelt, Maryland
National Aeronautics and
Space Administration
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CM FOREWORD
This document is a Robotic Lunar Exploration Program (RLEP) Configuration Management
(CM)-controlled document. Changes to this document require prior approval of the RLEP
Program (or specific project if document only applies at project level) Manager. Proposed
changes shall be submitted to the RLEP CM Office (CMO), along with supportive material
justifying the proposed change. Changes to this document will be made by complete revision.
Questions or comments concerning this document should be addressed to:
RLEP Configuration Manager (TBD)
RLEP Configuration Management Office
Mail Stop 430
Goddard Space Flight Center
Greenbelt, Maryland 20771
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Signature Page
Prepared by:
Michael Xapsos
LRO Radiation Lead
Code 561
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Date
Janet Barth
Associate Branch Head
Code 561
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Christian Poivey
LRO Radiation
Code 561
Reviewed by:
Michael Pryzby
LRO Systems Engineer
Code 431
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Philip Luers
RLEP Avionics Systems Engineer
Code 561
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Approved by:
Craig Tooley
LRO Project Manager
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Concurred by:
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ROBOTIC LUNAR EXPLORATION PROGRAM
DOCUMENT CHANGE RECORD
REV
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List of TBDs/TBRs
Item
No.
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Summary
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TABLE OF CONTENTS
Page
1.0
Introduction .................................................................................................................... 1-1
2.0
Radiation Environment ................................................................................................. 2-1
3.0
Description of Radiation Effects ................................................................................... 3-1
4.0
The LRO Mission ........................................................................................................... 4-3
5.0
Total Dose and Degradation ......................................................................................... 5-4
5.1
Degradation Environment .................................................................................... 5-4
5.1.1 The Plasma Environment ......................................................................... 5-4
5.1.2 High Energy Particles – Spacecraft Incident Fluences ............................ 5-4
5.1.3 High Energy Particles – Shielded Fluences ............................................. 5-8
5.2
Total Dose Estimates ........................................................................................... 5-9
5.2.1 Top Level Ionizing Dose Requirement .................................................... 5-9
5.2.2 Dose at Specific Spacecraft Locations ................................................... 5-10
5.3
displacement Damage Estimates........................................................................ 5-11
6.0
Single Event Effects Analysis ...................................................................................... 6-11
6.1
Heavy Ion Induced Single Event Effects ........................................................... 6-11
6.1.1 Galactic Cosmic Rays ............................................................................ 6-12
6.1.2 Solar Heavy Ions .................................................................................... 6-12
6.2
Proton Induced Single Event Effects ................................................................. 6-13
6.2.1 Trapped Protons ..................................................................................... 6-13
6.2.2 Neutrons ................................................................................................. 6-14
6.2.3 Solar Protons .......................................................................................... 6-14
7.0
Spacecraft Charging and Discharging ....................................................................... 7-14
8.0
Summary ....................................................................................................................... 8-15
9.0
References ..................................................................................................................... 9-15
Appendix A. Tables A-1 through A-10 ........................................................................................1
Appendix B. Abbreviations and Acronyms ..............................................................................13
ii
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LIST OF FIGURES
Figure
Page
Figure 4-1. Projection of the Solar Activity During the LRO Mission ...................................... 4-4
Figure 5-1. Solar Proton Fluences for 1 Solar Active Year for Various Confidence Levels ..... 5-5
Figure 5-2. Solar proton fluences for 2 solar active years for various confidence levels ........... 5-6
Figure 5-3. Solar proton fluences for 3 solar active years for various confidence levels ........... 5-6
Figure 5-4. Solar proton fluences for 4 solar active years for various confidence levels ........... 5-7
Figure 5-5. Solar proton fluences for 5 solar active years for various confidence levels ........... 5-7
Figure 5-6. Mission solar proton fluences for 1 to 5 years missions .......................................... 5-8
Figure 5-7. Shielded solar proton energy spectra for 100 mils Aluminum, 1 to 5 year mission 5-9
Figure 5-8. Total ionizing dose from solar proton events ......................................................... 5-10
Figure 6-1. Integral LET spectra are shown for galactic cosmic ray ions hydrogen through
uranium. ..................................................................................................................................... 6-12
Figure 6-2. Integral LET spectra are shown for hydrogen through uranium for the October 1989
solar particle event. .................................................................................................................... 6-13
Figure 6-3. Solar proton fluxes for single event effects evaluation. ......................................... 6-14
LIST OF TABLES
Table
Page
Table A-1. Spacecraft Incident Solar Proton Fluences for 1 Solar Active Year ........................... 1
Table A-2. Spacecraft Incident Solar Proton Fluences for 2 Solar Active Years .......................... 2
Table A-3. Spacecraft Incident Solar Proton Fluences for 3 Solar Active Years .......................... 3
Table A-4. Spacecraft Incident Solar Proton Fluences for 4 Solar Active Years .......................... 4
Table A-5. Spacecraft Incident Solar Proton Fluences for 5 Solar Active Years .......................... 5
Table A-6. Integral Solar Proton Fluence Levels Behind Solid Sphere Aluminum Shields ......... 6
iii
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Table A-7. Total Ionizing Dose at the Center of Aluminum Spheres Due to Solar Proton Events 7
Table A-8. Integral LET Spectrum for Interplanetary Galactic Cosmic Rays (Z=1-92) ............... 8
Table A-9. Integral LET Spectrum for the October 1989 Solar Particle Event (Z=1-92) ........... 10
Table A-10 Differential Proton Fluxes for the October 1989 Solar Particle Event ...................... 12
iv
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INTRODUCTION
The purpose of this document is to define the radiation environment for the evaluation of
degradation due to total ionizing and non-ionizing dose and of single event effects (SEEs) for the
Lunar Reconnaissance Orbiter (LRO). The analysis takes into account the radiation exposure for
one to five-year missions at the 50 km polar lunar orbit and assumes a launch date in 2008
according to the preliminary mission profile. The transfer trajectory out to lunar orbit will last
about 4 days. This evaluation does not include the impact of passing through the Van Allen belts
during the transfer orbit. Generally, transfer trajectories do not contribute significantly to
degradation effects; however, single event effects and deep dielectric charging effects must be
taken into consideration especially if critical maneuvers are planned during the Van Allen belt
pass.
2.0
RADIATION ENVIRONMENT
The natural space radiation environment of concern for damage to spacecraft electronics is
classified into two populations, 1) the transient particles which include protons and heavier ions
of all of the elements of the periodic table, and 2) the trapped particles which include protons,
electrons and heavier ions. The trapped electrons have energies up to about 10 MeV and the
trapped protons and heavier ions have energies up to 100s of MeV. The transient radiation
consists of galactic cosmic ray particles and particles from solar events (coronal mass ejections
and flares). The cosmic rays have low-level fluxes with energies up to TeV. The solar eruptions
periodically produce energetic protons, alpha particles, heavy ions, and electrons. The solar
protons have energies up to 100’s MeV and the heavier ions reach the GeV range. All particle
fluxes are isotropic and omnidirectional to the first order.
Space also contains low energy plasma of electrons and protons with fluxes up to 1012 cm2/sec.
The plasmasphere environment and the low energy (< 0.1 MeV) component of the charged
particles are a concern in the near-earth environment. In the outer regions of the magnetosphere
and in interplanetary space, the plasma is associated with the solar wind. Because of its low
energy, thin layers of material easily stop the plasma so it is not a hazard to most spacecraft
electronics. However, it is damaging to surface materials and differentials in the plasma
environment can contribute to spacecraft surface charging and discharging problems [1,2].
3.0
DESCRIPTION OF RADIATION EFFECTS
Radiation effects that are important to consider for instrument and spacecraft design fall roughly
into three categories: degradation from total ionizing dose (TID), degradation from non-ionizing
energy loss (NIEL), and single event effects. Total ionizing dose in electronics is a cumulative,
long-term degradation mechanism due to ionizing radiation—mainly primary protons and
electrons and secondary particles arising from interactions between these primary particles and
spacecraft materials. It causes threshold shifts, leakage current and timing skews. The effect first
appears as parametric degradation of the device and ultimately results in functional failure. It is
possible to reduce TID with shielding material that absorbs most electrons and lower energy
protons. As shielding is increased, shielding effectiveness decreases because of the difficulty in
3-1
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slowing down the higher energy protons. When a manufacturer advertises a part as “rad-hard”,
he is almost always referring to its total ionizing dose characteristics. Rad-hard does not usually
imply that the part is hard to non-ionizing dose or single event effects. In some cases, a “radhard” part may perform significantly worse in the space radiation environment than in the test
environment (e.g. Enhanced Low Dose Rate Sensitivity in linear bipolar devices.)
Displacement damage is cumulative, long-term non-ionizing damage due to protons, electrons,
and neutrons. These particles produce defects in optical materials that result in charge transfer
degradation. Displacement damage affects the performance of optocouplers (often a component
in power devices), solar cells, CCDs, and linear bipolar devices. The effectiveness of shielding
depends on the location of the device. For example, coverglasses over solar cells reduce electron
damage and proton damage by absorbing the low energy particles. Increasing shielding beyond a
critical threshold, however, is not usually effective for optoelectronic components because the
high-energy protons penetrate the most feasible spacecraft electronic enclosures. For detectors in
instruments it is necessary to understand the instrument technology and geometry to determine
the vulnerability to the environment.
Single event effects (SEE) result from ionization by a single charged particle as it passes through
a sensitive junction of an electronic device. SEE are caused by heavier ions, but for some
devices, protons and neutrons can also contribute. In some cases SEEs are induced through direct
ionization by the proton, but in most instances for protons and in all instances for neutrons,
induced effects result from secondary particles produced when the proton or neutron interacts
with a nucleus in the device material. Some single event effects are non-destructive, as in the
case of single event upsets (SEUs), single event transients (SETs), multiple bit errors (MBEs),
single event hard errors (SHEs), etc. Single event effects can also be destructive as in the case of
single event latchups (SELs), single event gate ruptures (SEGRs), and single event burnouts
(SEBs). The severity of the effect can range from noisy data to loss of the mission, depending on
the type of effect and the criticality of the system in which it occurs. Shielding is generally not an
effective mitigator for single event effects, which are often induced by very penetrating highenergy particles. The preferred method for dealing with destructive failures is to use SEE-hard
parts. When SEE-hard parts are not available, latchup protection circuitry is sometimes used in
conjunction with failure mode analysis. (Note: Care is necessary when using SEL protection
circuitry, because SEL may damage a microcircuit and reduce its reliability even when it does
not cause outright failure.) For non-destructive effects, mitigation takes the form of errordetection and correction codes (EDACs), filtering circuitry, etc.
Total ionizing dose is primarily caused by protons and electrons trapped in the Van Allen belts
and solar event protons. As electrons are slowed down, their interactions with orbital electrons of
the shielding material produce a secondary photon radiation known as bremsstrahlung.
Generally, the dose due to galactic cosmic ray ions and proton secondaries is negligible
compared to other sources. For surface degradation, it is also important to include the effects of
very low energy particles.
3-2
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Single event effects can be induced by heavy ions (solar events and galactic cosmic rays) and, in
some devices, protons (trapped and solar events) and neutrons. Displacement damage is
primarily due to trapped and solar protons and also neutrons. High-energy electrons can also
contribute to displacement damage, especially for lightly shielded applications. Spacecraft
charging can occur on the surface of the spacecraft due to low energy electrons. Deep dielectric
charging occurs when high-energy electrons penetrate the spacecraft and collect in dielectric
materials.
4.0
THE LRO MISSION
The LRO spacecraft will be transferred out to its final lunar orbit via a four-day trajectory. While
in the transfer, LRO will pass through the trapped proton and electron belts. During the transfer
trajectory, LRO will also encounter varying levels of galactic cosmic ray heavy ions and possibly
protons and heavier ions from solar events. These exposures could result in single event effects
during some maneuvers as well as a deep dielectric charging risk but will not contribute to
significant total dose degradation effects.
Once LRO reaches its final orbit, its mission requirement is 1 to 5 years. With its expected 2008
launch year, the LRO mission will occur during the active phase of the solar cycle. During the
active phase of the sun, the likelihood that the spacecraft will be exposed to particles from solar
events (either solar flare or coronal mass ejections) increases significantly. Figure 4-1 shows a
projection of the solar cycle during the LRO mission, based on the solar activity data of solar
cycles 22 and 23. The lunar orbit radiation environment encountered by the LRO will consist of
protons and heavier ions from solar events, galactic cosmic ray heavy ions, neutrons emitted by
the lunar soil, and solar wind plasma consisting of low energy protons, electrons, and heavier
ions.

Neutrons in space are produced by interactions of primary particles with spacecraft materials and planet soils. In avionics
applications it is also necessary to consider neutrons that are produced by interactions of primary particles with the atmosphere.
4-3
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Figure 4-1. Projection of the Solar Activity During the LRO Mission
5.0
TOTAL DOSE AND DEGRADATION
The total ionizing dose accumulation causes performance degradation and failure on memories,
power converters, etc. Non-ionizing energy loss in materials (atomic displacement damage)
causes degradation of solar cells, optoelectronics, and detectors. The low energy particles also
contribute to the erosion of surfaces.
5.1
DEGRADATION ENVIRONMENT
5.1.1 The Plasma Environment
At the LRO final orbit, low energy particles from the solar wind plasma inside and outside the
magnetotail contribute to the degradation of surface materials and also cause charging effects.
These charging effects should be considered in the spacecraft design. However, the plasma
environment does not contribute to significant degradation effects.
5.1.2 High Energy Particles – Spacecraft Incident Fluences
The spacecraft incident proton fluence levels given in this document are most often used for
standard solar cell analyses that take into account the coverglass thickness of the cell. There are
four possible sources of high energy particles: trapped protons and trapped electrons encountered
in the transfer trajectory, neutrons emitted by the lunar soil, and protons from solar events that
can occur anytime during the one to five solar active years of the mission. The trapped particles
encountered in the transfer trajectory are usually not a factor in degradation analyses. The
neutrons emitted by the lunar soil are also not a factor in degradation analysis, because their
intensity is very small compared to those of solar protons [3]. The proton fluence levels are also
5-4
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used to determine displacement damage effects, however, most analysis methods require that the
surface incident particles be transported through the materials surrounding the sensitive
components. The proton fluences behind nominal aluminum shield thicknesses are given in
Section V.A.3.
The solar proton levels were estimated from the Emission of Solar Protons (ESP) model [4]. The
ESP model is based on satellite data from solar cycles 20, 21, and 22. The distribution of the
fluences for the events is obtained from maximum entropy theory, and design limits in the worst
case models are obtained from extreme value theory.
Total integral solar proton fluences were estimated for 1 to 5 solar active years. Tables A-11
through A-5 give the fluence levels as a function of particle energy for 85, 90, 95, and 99%
confidence levels. Figures 5-1 through 5-5 are plots of the energy-fluence spectra for the given
confidence levels. The energies are threshold energies, given in units of >MeV and the fluences
are integral fluences in units of protons/cm2. These values do not include a design margin. The
solar proton predictions are based on probability distributions and are therefore not linear with
increasing time. Only the mean value of the distribution increases linearly. Therefore, these
estimates at high confidence levels may be invalid if extrapolated to longer or shorter mission
durations.
Solar Proton Fluence for Various Confidence Levels
1 Solar Active Year, ESP Model, Unattenuated
85%
90%
95%
99%
1.00E+11
1.00E+10
2
Proton Fluence (#/cm - 1 solar active year)
1.00E+12
1.00E+09
1.00E+08
1.00E+07
0
50
100
150
200
250
300
Energy (> MeV)
Figure 5-1. Solar Proton Fluences for 1 Solar Active Year for Various Confidence Levels
5-5
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Solar Proton Fluence for Various Confidence Levels
2 Solar Active Years, ESP Model, Unattenuated
85%
90%
95%
99%
1.00E+11
1.00E+10
2
Proton Fluence (#/cm - 2 solar active years)
1.00E+12
1.00E+09
1.00E+08
1.00E+07
0
50
100
150
200
250
300
Energy (> MeV)
Figure 5-2. Solar proton fluences for 2 solar active years for various confidence levels
Solar Proton Fluence for Various Confidence Levels
3 Solar Active Years, ESP Model, Unattenuated
85%
90%
95%
99%
1.00E+11
1.00E+10
2
Proton Fluence (#/cm - 3 solar active years)
1.00E+12
1.00E+09
1.00E+08
1.00E+07
0
50
100
150
200
250
300
Energy (> MeV)
Figure 5-3. Solar proton fluences for 3 solar active years for various confidence levels
5-6
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Solar Proton Fluence for Various Confidence Levels
4 Solar Active Years, ESP Model, Unattenuated
85%
90%
95%
99%
1.00E+11
1.00E+10
2
Proton Fluence (#/cm - 4 solar active years)
1.00E+12
1.00E+09
1.00E+08
1.00E+07
0
50
100
150
200
250
300
Energy (> MeV)
.
Figure 5-4. Solar proton fluences for 4 solar active years for various confidence levels
Solar Proton Fluence for Various Confidence Levels
5 Solar Active Years, ESP Model, Unattenuated
85%
90%
95%
99%
1.00E+11
1.00E+10
2
Proton Fluence (#/cm - 5 solar active years)
1.00E+12
1.00E+09
1.00E+08
1.00E+07
0
50
100
150
200
250
300
Energy (> MeV)
Figure 5-5. Solar proton fluences for 5 solar active years for various confidence levels
5-7
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Figure 5-6 gives the mission fluences for 1 to 5 years that will be considered. For one-year
mission we use a 95% confidence level, and for two to five year missions we use a 90%
confidence level. This recommended choice in confidence levels results because the accuracy of
the statistical model improves for longer periods of time.
Mission Solar Proton Fluence for 1 to 5 years
ESP Model, Unattenuated
1.00E+12
1 year, 95%
2 years, 90%
3 years, 90%
4 years, 90%
5 years, 90%
2
Mission Fluence (#/cm )
1.00E+11
1.00E+10
1.00E+09
1.00E+08
1.00E+07
0
50
100
150
200
250
300
Energy (> MeV)
Figure 5-6. Mission solar proton fluences for 1 to 5 years missions
5.1.3 High Energy Particles – Shielded Fluences
Evaluation of non-ionizing energy loss damage requires the use of shielded fluence levels. For
this analysis, nominal shielding thicknesses of 100 mils of aluminum were used for generic solid
sphere geometry. The mission spacecraft incident, solar proton estimates for the 1 to 5 year
missions were transported through the shield thickness to obtain fluence estimates behind the
shielding. Table A-6 gives the degraded energy spectra. The spectra are plotted in Figure 5-7.
It can be seen from the figures that even though low-energy particles are absorbed by the
shielding, the low energy range of the spectrum is filled in by the higher energy protons as they
are degraded by passing through the material.
5-8
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Mission Shielded Integral Solar Proton Fluence for 100 mils
(2.54 mm) Aluminum - Value do not include Design Margins
Solar Protons Fluence (#/cm2)
1.00E+11
1 year
2 years
3 years
4 years
5 years
1.00E+10
1.00E+09
1.00E+08
1.00E+07
0.1
1.0
10.0
100.0
1000.0
Energy (> MeV)
Figure 5-7. Shielded solar proton energy spectra for 100 mils Aluminum, 1 to 5 year
mission
5.2
TOTAL DOSE ESTIMATES
5.2.1 Top Level Ionizing Dose Requirement
Doses are calculated from the surface incident integral fluences as a function of aluminum shield
thickness for a simple geometry. The geometry model used for spacecraft applications is the
solid sphere. The solid sphere doses represent an upper boundary for the dose inside an actual
spacecraft and are used as a top-level requirement. In cases where the amount of shielding
surrounding a sensitive location is difficult to estimate, a more detailed analysis of the geometry
of the spacecraft structure may be necessary to evaluate the expected dose levels. This is done
by modeling the electronic boxes or instruments and the spacecraft structure. The amount of
shielding surrounding selected sensitive locations is estimated using solid angle sectoring and 3dimensional ray tracing. Doses obtained by sectoring methods must be verified for at least 510% of the sensitive locations with full Monte Carlo simulations of particle trajectories through
the structure for many histories.
Table A-7 and Figure 5-8 give the top-level total ionizing dose requirement for the 1 to 5 year
LRO mission. The doses are calculated here as a function of aluminum shield thickness in units
of krads in silicon. For the nominal 100 mils of equivalent aluminum shielding and the 5 years
5-9
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mission, the dose requirement is about 14 krad-Si with no design margin. A minimum design
margin of x 2 is recommended.
Total Dose at the Center of Solid Aluminum Spheres - Top Level
Requirement - Values do not include Design Margin
1000.00
1 year
2 years
3 years
4 years
5 years
Dose (krad-Si)
100.00
10.00
1.00
0.10
0.01
0
200
400
600
800
1000
1200
1400
1600
Aluminum Shield Thickness (mils)
Figure 5-8. Total ionizing dose from solar proton events
5.2.2 Dose at Specific Spacecraft Locations
In cases where parts cannot meet the top level design requirement and a “harder” part cannot be
substituted, it is often beneficial to employ more accurate methods of determining the dose
exposure for some spacecraft components to qualify the parts. One such method for calculating
total dose, solid angle sectoring/3-dimensional ray tracing, is accomplished in three steps:
1) Model the spacecraft structure:
-develop a 3-D model of the spacecraft structures and components
-develop a material library
-define sensitive locations
2) Model the radiation environment:
5-10
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-define the spacecraft incident radiation environment
-develop a particle attenuation model using theoretical shielding configurations
(similar to dose-depth curves).
3) Obtain results for each sensitive location:
-divide the structural model into solid angle sectors
-ray trace through the sectors to calculate the material mass distribution
-use the ray trace results to calculate total doses from the particle attenuation model.
Once the basic structural model has been defined, total doses can be obtained for any location in
the spacecraft in a short time (in comparison to Monte Carlo methods). The value of dose
mitigation measures can be accurately evaluated be adding the changes to the model and
recalculating the total dose. For spacecraft with strict weight budgets, the 3-D ray trace method,
the total dose design requirement can be defined at a box or instrument level avoiding
unnecessary use of expensive or increasingly unavailable radiation hardened parts.
As the design of the LRO evolves, it may become necessary to estimate the doses at specific
locations in the spacecraft or instruments. Often the dose requirement can be met by modeling
the surrounding electronic box only or by modeling only the instrument.
5.3
DISPLACEMENT DAMAGE ESTIMATES
Total non-ionizing energy loss damage is evaluated by combining the shielded proton energy
spectra given Section V.A.2 with the NIEL Non Ionizing Energy Loss (NIEL) response curves
for the material and the results of laboratory radiation of the devices sensitive to atomic
displacement damage. The level of the hazard is highly dependent on the device type and can be
process specific. For the LRO mission, it is important to keep in mind that some optoelectronic
devices experience enough damage during one large solar proton event to cause the device to
fail. It is necessary that the parts list screening for radiation also include a check for devices that
are susceptible to displacement damage.
6.0
SINGLE EVENT EFFECTS ANALYSIS
6.1
HEAVY ION INDUCED SINGLE EVENT EFFECTS
Some electronic devices are susceptible to single event effects (SEEs), e.g., single event upsets,
single event latch-up, single event burn-out. Since heavy ions such as GCR and solar heavy ions
cause SEEs by the direct deposit of charge, the metric used to describe SEEs is the ion’s linear
energy transfer (LET). The LET is the energy lost by the ion per unit path length in the material
of interest. In order to parameterize SEEs in terms of LET, the heavy ion abundances and energy
distributions in the environment are converted to LET spectra. Once specific parts are selected
for the mission and, if necessary, characterized by laboratory testing, the LET spectra for the
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heavy ions in the space radiation environment are integrated with the device characterization to
calculate SEE rates.
6.1.1 Galactic Cosmic Rays
The cosmic ray fluxes for elements hydrogen through uranium were used to calculate daily LET
spectra for a nominal shielding thickness of 100 mils aluminum. Results are given in Table A-8
and Figure 6-1. The range of the cosmic ray abundances is bounded by the extrema of the solar
active and inactive phases of the solar cycle with the highest values occurring during the solar
inactive phase and the lowest during the solar active phase. The LET fluence values are given
for the highest and lowest point of the solar cycle. The CREME96 [5] model was used to obtain
the cosmic ray heavy ion abundances. This model has an accuracy of 25-40%. For the LRO SEE
analysis, we recommend to use the highest fluxes.
Integral LET Spectra at 1AU (Z=1-92) for Interplanetary Galactic Cosmic Rays
100 mils Aluminum Shielding, CREME96
1.00E+06
1.00E+05
1.00E+04
Solar minimum
1.00E+03
Solar maximum
1.00E+02
LET fluence (#/cm2-day)
1.00E+01
1.00E+00
1.00E-01
1.00E-02
1.00E-03
1.00E-04
1.00E-05
1.00E-06
1.00E-07
1.00E-08
1.00E-09
1.00E-10
1.E-03
1.E-02
1.E-01
1.E+00
1.E+01
1.E+02
1.E+03
LET energy (MeV-cm2/mg)
Figure 6-1. Integral LET spectra are shown for galactic cosmic ray ions hydrogen through
uranium.
6.1.2 Solar Heavy Ions
The heavy ions from solar flares and coronal mass ejections can also produce single event
effects. The solar event fluxes for the elements hydrogen through uranium were used to
calculate daily LET spectra for 100 mils aluminum shielding in units of average LET flux per
second. The intensity of the fluxes varies over the duration of an event; therefore, values are
averaged over the worst week of the solar cycle, the worst day of the solar cycle, and the peak of
the October 1989 solar event. Table A-9 and Figure 6-2 give the worst case solar heavy ion
6-12
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LET predictions for the LRO mission, obtained from CREME96. An uncertainty factor for the
solar heavy ion model has not been released.
Integral LET Spectra at 1 AU (Z=1-92) for Interplanetary Solar Particle Events 100 mils
Aluminum Shielding, CREME96
1.00E+06
1.00E+05
1.00E+04
Average Over Peak
1.00E+03
Average Over Worst Day
1.00E+02
Average Over Worst Week
LET Fluence (#/cm2-s)
1.00E+01
1.00E+00
1.00E-01
1.00E-02
1.00E-03
1.00E-04
1.00E-05
1.00E-06
1.00E-07
1.00E-08
1.00E-09
1.00E-10
1.00E-11
1.00E-03
1.00E-02
1.00E-01
1.00E+00
1.00E+01
1.00E+02
1.00E+03
LET Energy (MeV-cm2/mg)
Figure 6-2. Integral LET spectra are shown for hydrogen through uranium for the
October 1989 solar particle event.
6.2
PROTON INDUCED SINGLE EVENT EFFECTS
In some devices, single event effects are also induced by protons and neutrons. In most cases,
protons do not generate sufficient ionization (LET < 1 MeV-cm2 /mg) to produce the critical
charge necessary for SEEs to occur in most electronics. More typically, protons cause SEEs
through secondary particles via nuclear interactions, that is, spallation and fractionation products.
Because the proton energy is important in the production (and not the LET) of the secondary
particles that cause the SEEs, device sensitivity to these particles is typically expressed as a
function of proton energy rather than LET. Neutrons can only cause SEEs through secondary
particles via nuclear interactions, that is, spallation and fractionation products.
6.2.1 Trapped Protons
Trapped protons can be a concern for single event effects during the transfer trajectory passes
through the trapped particle radiation belts. The proton fluxes in the intense regions of the belts
reach levels that are high enough to pose a significant risk for upsets or latchups. The timing of
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critical operations during the transfer trajectory should be analyzed to determine the trapped
proton environment at the time of the operation.
6.2.2 Neutrons
The neutron fluxes at the LRO 50 km altitude above moon surface are very small compared to
those of solar protons [3]. Therefore, neutrons are not a SEE concern for most LRO electronics
parts. They may be a concern for some instrument detectors as they will add noise.
6.2.3 Solar Protons
Protons from solar events can also be a single event effects hazard for the LRO spacecraft.
These enhanced levels of protons could occur anytime during the 1 to 5 year mission. As with
the worst case solar heavy ion LET, solar proton fluxes are averaged over worst day, worst week,
and the peak of the October 1989 solar event. The worst case proton flux averages for a nominal
100 mils of shielding are given in Table A-10 and are shown in Figure 6-3.
D iff e re n ti a l S o la r P r o t o n E v e n t F l u x e s a t 1 A U
1 0 0 m il s A lu m i n u m S h ie ld in g , C R E M E 9 6
1.0E + 05
A v e ra g e O v e r P e a k
1.0E + 04
A v e ra g e O v e r W o rs t D a y
A v e ra g e O v e r W o rs t W e e k
1.0E + 02
2
P a rt ic l e s (# / c m/ s /M e V )
1.0E + 03
1.0E + 01
1.0E + 00
1 .0 E - 0 1
1 .0 E - 0 2
V a lu e s D o N o t I n c lu d e D e s ig n M a r g in
1 .0 E - 0 3
1
10
10 0
1 000
E n e rg y ( M e V )
Figure 6-3. Solar proton fluxes for single event effects evaluation.
7.0
SPACECRAFT CHARGING AND DISCHARGING
Surface charging and deep dielectric charging must also be evaluated for the LRO mission. Both
are potential problems in transfer trajectory through the Van Allen belts. During the pass
through the belts, the spacecraft can accumulate high levels of electron build-up on spacecraft
surfaces (low energy electrons) in the dielectrics (high energy electrons). Surface charging will
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also be a concern during the entire mission when the spacecraft reaches its final orbit due to the
plasma environment.
8.0
SUMMARY
A top-level radiation environment specification was presented for the LRO mission. Although
the environment is considered “moderate”, the environment poses challenges to mission
designers because of its highly variable nature caused by activity on the sun.
Spacecraft and instrument designers must be made aware that some newer technologies and
commercial-off-the-shelf (COTS) devices are very soft to radiation effects. COTS devices that
lose functionality at 5 krads of dose are not uncommon. One extremely large solar proton event
can cause enough displacement damage degradation in some optocoupler devices to cause
failure. Increasingly, single event effects require careful part selection and mitigation schemes.
With its full exposure to galactic cosmic ray heavy ions and particles from solar events, LRO
must have a carefully planned radiation engineering program.
9.0
REFERENCES
[1]
A. Holmes-Siedle and L. Adams, Handbook of Radiation Effects, p. 16, Oxford
University Press, Oxford, 1993.
[2]
A. R. Frederickson, “Upsets Related to Spacecraft Charging,” IEEE Trans. on Nucl.
Science, Vol. 43, No. 2, pp. 426-441, April 1996.
[3]
R. C. Elphic, W. C. Feldman, D. J. Lawrence, O. M. Gasnault, S. Maurice, R. Little, T. H.
Prettyman, and A. H. Binder, “The Lunar Neutron Leakage Flux and its Measurement by
Lunar Prospector Neutron Spectrometers,” XXXII Lunar and Planetary Science
Conference, 2001.
[4]
M. A. Xapsos, J. L. Barth, E. G. Stassinopoulos, E.A. Burke and G. B. Gee, “Model for
Emission of Solar Protons (ESP) – Cumulative and Worst Case Event Fluences”, Marshall
Space Flight Center, Huntsville, AL, NASA Report TP-1999-209763, Dec. 1999.
[5]
A. J. Tylka, J. H. Adams, Jr., P. R. Boberg, W. F. Dietrich, E.O. Flueckiger, E.L. Petersen,
M.A. Shea, D.F. Smart, and E.C. Smith, “CREME96: A Revision of the Cosmic Ray
Effects on Micro-Electronics Code: to be published in IEEE Trans. On Nuc. Sci.,
December 1997.
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Appendix A. Tables A-1 through A-10
Proton
Energy
(>MeV)
1
3
5
7
10
15
20
25
30
35
40
45
50
55
60
70
80
90
100
125
150
175
200
225
250
275
300
80
1.26E+11
4.43E+10
2.47E+10
1.61E+10
9.84E+09
5.35E+09
3.34E+09
2.27E+09
1.63E+09
1.22E+09
9.40E+08
7.41E+08
5.96E+08
4.87E+08
4.04E+08
2.87E+08
2.11E+08
1.60E+08
1.24E+08
7.45E+07
4.82E+07
3.30E+07
2.36E+07
1.74E+07
1.32E+07
1.02E+07
7.99E+06
Proton Fluence(cm^-2)
Confidence Levels(%)
85
90
95
1.48E+11 1.81E+11 2.43E+11
5.58E+10 7.46E+10 1.15E+11
3.21E+10 4.47E+10 7.32E+10
2.14E+10 3.06E+10 5.22E+10
1.34E+10 1.97E+10 3.51E+10
7.46E+09 1.14E+10 2.11E+10
4.75E+09 7.37E+09 1.42E+10
3.27E+09 5.16E+09 1.02E+10
2.37E+09 3.79E+09 7.59E+09
1.78E+09 2.88E+09 5.86E+09
1.38E+09 2.25E+09 4.64E+09
1.10E+09 1.80E+09 3.75E+09
8.88E+08 1.46E+09 3.08E+09
7.29E+08 1.21E+09 2.56E+09
6.06E+08 1.01E+09 2.15E+09
4.33E+08 7.27E+08 1.57E+09
3.20E+08 5.40E+08 1.17E+09
2.43E+08 4.12E+08 9.03E+08
1.89E+08 3.22E+08 7.09E+08
1.14E+08 1.94E+08 4.27E+08
7.37E+07 1.26E+08 2.77E+08
5.04E+07 8.60E+07 1.89E+08
3.61E+07 6.15E+07 1.35E+08
2.66E+07 4.53E+07 9.99E+07
2.01E+07 3.43E+07 7.55E+07
1.55E+07 2.65E+07 5.83E+07
1.22E+07 2.08E+07 4.58E+07
99
4.23E+11
2.56E+11
1.84E+11
1.42E+11
1.03E+11
6.78E+10
4.83E+10
3.61E+10
2.80E+10
2.22E+10
1.80E+10
1.48E+10
1.24E+10
1.04E+10
8.89E+09
6.61E+09
5.05E+09
3.93E+09
3.12E+09
1.88E+09
1.22E+09
8.34E+08
5.97E+08
4.40E+08
3.33E+08
2.57E+08
2.02E+08
Values Do Not Include Design Margins
Table A-1. Spacecraft Incident Solar Proton Fluences for 1 Solar Active Year
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Radiation Environment for the LRO
Proton
Energy
(>MeV)
1
3
5
7
10
15
20
25
30
35
40
45
50
55
60
70
80
90
100
125
150
175
200
225
250
275
300
80
2.47E+11
9.33E+10
5.39E+10
3.59E+10
2.25E+10
1.25E+10
7.89E+09
5.41E+09
3.91E+09
2.93E+09
2.27E+09
1.79E+09
1.45E+09
1.18E+09
9.83E+08
7.00E+08
5.16E+08
3.91E+08
3.03E+08
1.83E+08
1.18E+08
8.10E+07
5.79E+07
4.27E+07
3.23E+07
2.49E+07
1.96E+07
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Proton Fluence (cm^-2)
Confidence Levels(%)
85
90
95
2.79E+11 3.24E+11 4.06E+11
1.13E+11 1.42E+11 2.02E+11
6.72E+10 8.87E+10 1.34E+11
4.58E+10 6.23E+10 9.82E+10
2.94E+10 4.11E+10 6.78E+10
1.67E+10 2.42E+10 4.20E+10
1.08E+10 1.60E+10 2.87E+10
7.50E+09 1.13E+10 2.08E+10
5.47E+09 8.36E+09 1.57E+10
4.14E+09 6.40E+09 1.22E+10
3.23E+09 5.03E+09 9.71E+09
2.57E+09 4.03E+09 7.88E+09
2.08E+09 3.29E+09 6.49E+09
1.71E+09 2.72E+09 5.41E+09
1.43E+09 2.28E+09 4.57E+09
1.02E+09 1.65E+09 3.34E+09
7.58E+08 1.23E+09 2.52E+09
5.77E+08 9.40E+08 1.94E+09
4.49E+08 7.34E+08 1.53E+09
2.71E+08 4.43E+08 9.20E+08
1.75E+08 2.87E+08 5.95E+08
1.20E+08 1.96E+08 4.08E+08
8.57E+07 1.40E+08 2.92E+08
6.32E+07 1.04E+08 2.15E+08
4.78E+07 7.83E+07 1.63E+08
3.69E+07 6.04E+07 1.25E+08
2.90E+07 4.75E+07 9.87E+07
99
6.21E+11
3.89E+11
2.90E+11
2.30E+11
1.73E+11
1.18E+11
8.56E+10
6.51E+10
5.10E+10
4.08E+10
3.34E+10
2.76E+10
2.32E+10
1.97E+10
1.68E+10
1.26E+10
9.65E+09
7.55E+09
6.01E+09
3.62E+09
2.35E+09
1.61E+09
1.15E+09
8.47E+08
6.40E+08
4.94E+08
3.89E+08
Values Do Not Include Design Margins
Table A-2. Spacecraft Incident Solar Proton Fluences for 2 Solar Active Years
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Proton
Energy
(>MeV)
1
3
5
7
10
15
20
25
30
35
40
45
50
55
60
70
80
90
100
125
150
175
200
225
250
275
300
80
3.61E+11
1.41E+11
8.32E+10
5.63E+10
3.58E+10
2.01E+10
1.29E+10
8.88E+09
6.44E+09
4.85E+09
3.76E+09
2.98E+09
2.41E+09
1.98E+09
1.64E+09
1.17E+09
8.65E+08
6.56E+08
5.09E+08
3.07E+08
1.99E+08
1.36E+08
9.73E+07
7.18E+07
5.43E+07
4.19E+07
3.29E+07
431-SPEC-000020
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Proton Fluence(cm^-2)
Confidence Levels(%)
85
90
95
3.99E+11 4.54E+11 5.48E+11
1.66E+11 2.04E+11 2.76E+11
1.01E+11 1.30E+11 1.87E+11
7.01E+10 9.23E+10 1.39E+11
4.56E+10 6.19E+10 9.75E+10
2.64E+10 3.71E+10 6.15E+10
1.72E+10 2.48E+10 4.25E+10
1.20E+10 1.76E+10 3.11E+10
8.83E+09 1.31E+10 2.36E+10
6.71E+09 1.01E+10 1.84E+10
5.24E+09 7.95E+09 1.47E+10
4.18E+09 6.39E+09 1.20E+10
3.40E+09 5.23E+09 9.92E+09
2.80E+09 4.33E+09 8.29E+09
2.33E+09 3.64E+09 7.01E+09
1.68E+09 2.63E+09 5.14E+09
1.24E+09 1.97E+09 3.88E+09
9.49E+08 1.51E+09 3.00E+09
7.39E+08 1.18E+09 2.36E+09
4.46E+08 7.12E+08 1.42E+09
2.88E+08 4.61E+08 9.22E+08
1.97E+08 3.15E+08 6.32E+08
1.41E+08 2.26E+08 4.52E+08
1.04E+08 1.66E+08 3.33E+08
7.87E+07 1.26E+08 2.52E+08
6.08E+07 9.71E+07 1.94E+08
4.78E+07 7.63E+07 1.53E+08
99
7.83E+11
4.88E+11
3.70E+11
2.98E+11
2.28E+11
1.59E+11
1.17E+11
8.99E+10
7.10E+10
5.72E+10
4.70E+10
3.91E+10
3.29E+10
2.80E+10
2.40E+10
1.80E+10
1.39E+10
1.09E+10
8.69E+09
5.24E+09
3.39E+09
2.32E+09
1.66E+09
1.22E+09
9.26E+08
7.15E+08
5.62E+08
Values Do Not Include Design Margins
Table A-3. Spacecraft Incident Solar Proton Fluences for 3 Solar Active Years
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Proton
Energy
(>MeV)
1
3
5
7
10
15
20
25
30
35
40
45
50
55
60
70
80
90
100
125
150
175
200
225
250
275
300
80
4.70E+11
1.87E+11
1.12E+11
7.68E+10
4.93E+10
2.81E+10
1.81E+10
1.25E+10
9.13E+09
6.90E+09
5.36E+09
4.26E+09
3.45E+09
2.83E+09
2.35E+09
1.68E+09
1.24E+09
9.44E+08
7.33E+08
4.42E+08
2.86E+08
1.96E+08
1.40E+08
1.03E+08
7.81E+07
6.03E+07
4.74E+07
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Proton Fluence(cm^-2)
Confidence Levels(%)
85
90
95
5.14E+11 5.76E+11 6.80E+11
2.17E+11 2.61E+11 3.42E+11
1.34E+11 1.68E+11 2.34E+11
9.38E+10 1.21E+11 1.76E+11
6.18E+10 8.20E+10 1.25E+11
3.62E+10 4.98E+10 7.98E+10
2.38E+10 3.35E+10 5.57E+10
1.67E+10 2.40E+10 4.10E+10
1.23E+10 1.79E+10 3.13E+10
9.38E+09 1.38E+10 2.45E+10
7.35E+09 1.09E+10 1.97E+10
5.87E+09 8.81E+09 1.61E+10
4.78E+09 7.22E+09 1.33E+10
3.94E+09 5.99E+09 1.11E+10
3.29E+09 5.03E+09 9.43E+09
2.37E+09 3.66E+09 6.94E+09
1.76E+09 2.74E+09 5.25E+09
1.34E+09 2.10E+09 4.06E+09
1.05E+09 1.64E+09 3.20E+09
6.32E+08 9.92E+08 1.93E+09
4.09E+08 6.42E+08 1.25E+09
2.80E+08 4.40E+08 8.56E+08
2.00E+08 3.14E+08 6.12E+08
1.48E+08 2.32E+08 4.52E+08
1.12E+08 1.75E+08 3.41E+08
8.62E+07 1.35E+08 2.64E+08
6.78E+07 1.06E+08 2.07E+08
99
9.30E+11
5.71E+11
4.37E+11
3.55E+11
2.75E+11
1.94E+11
1.44E+11
1.12E+11
8.89E+10
7.20E+10
5.94E+10
4.95E+10
4.18E+10
3.57E+10
3.06E+10
2.31E+10
1.78E+10
1.40E+10
1.12E+10
6.75E+09
4.37E+09
2.99E+09
2.14E+09
1.58E+09
1.19E+09
9.21E+08
7.24E+08
Values Do Not Include Design Margins
Table A-4. Spacecraft Incident Solar Proton Fluences for 4 Solar Active Years
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Radiation Environment for the LRO
Proton
Energy
(>MeV)
1
3
5
7
10
15
20
25
30
35
40
45
50
55
60
70
80
90
100
125
150
175
200
225
250
275
300
80
5.77E+11
2.32E+11
1.41E+11
9.70E+10
6.29E+10
3.62E+10
2.34E+10
1.63E+10
1.19E+10
9.03E+09
7.03E+09
5.59E+09
4.53E+09
3.73E+09
3.10E+09
2.22E+09
1.64E+09
1.25E+09
9.70E+08
5.85E+08
3.79E+08
2.59E+08
1.86E+08
1.37E+08
1.03E+08
7.98E+07
6.28E+07
431-SPEC-000020
Revision DRAFT
Proton Fluence(cm^-2)
Confidence Levels(%)
85
90
95
6.26E+11 6.93E+11 8.06E+11
2.66E+11 3.14E+11 4.04E+11
1.66E+11 2.04E+11 2.78E+11
1.17E+11 1.48E+11 2.10E+11
7.77E+10 1.01E+11 1.50E+11
4.60E+10 6.22E+10 9.72E+10
3.04E+10 4.21E+10 6.82E+10
2.15E+10 3.03E+10 5.05E+10
1.59E+10 2.27E+10 3.87E+10
1.21E+10 1.76E+10 3.05E+10
9.52E+09 1.39E+10 2.45E+10
7.62E+09 1.13E+10 2.00E+10
6.21E+09 9.24E+09 1.66E+10
5.13E+09 7.68E+09 1.40E+10
4.29E+09 6.46E+09 1.18E+10
3.09E+09 4.70E+09 8.72E+09
2.30E+09 3.52E+09 6.61E+09
1.76E+09 2.71E+09 5.12E+09
1.37E+09 2.12E+09 4.04E+09
8.27E+08 1.28E+09 2.44E+09
5.36E+08 8.28E+08 1.58E+09
3.67E+08 5.67E+08 1.08E+09
2.62E+08 4.05E+08 7.73E+08
1.93E+08 2.99E+08 5.70E+08
1.46E+08 2.26E+08 4.31E+08
1.13E+08 1.74E+08 3.33E+08
8.87E+07 1.37E+08 2.62E+08
99
1.07E+12
6.46E+11
4.95E+11
4.04E+11
3.15E+11
2.25E+11
1.69E+11
1.32E+11
1.05E+11
8.55E+10
7.08E+10
5.92E+10
5.01E+10
4.28E+10
3.68E+10
2.79E+10
2.15E+10
1.70E+10
1.36E+10
8.18E+09
5.30E+09
3.63E+09
2.59E+09
1.91E+09
1.45E+09
1.12E+09
8.78E+08
Values Do Not Include Design Margins
Table A-5. Spacecraft Incident Solar Proton Fluences for 5 Solar Active Years
A-5
CHECK WITH RLEP DATABASE AT:
http://vsde.gsfc.nasa.gov/index.jsp
TO VERIFY THAT THIS IS THE CORRECT VERSION PRIOR TO USE.
Radiation Environment for the LRO
Degraded
Energy
(> MeV)
0.10
0.13
0.16
0.20
0.25
0.32
0.40
0.50
0.63
0.79
1.00
1.26
1.58
2.00
2.51
3.16
3.98
5.01
6.31
7.94
10.00
12.60
15.80
20.00
25.10
31.60
39.80
50.10
63.10
79.40
100.00
126.00
158.00
200.00
251.00
431-SPEC-000020
Revision DRAFT
Shielded Solar Proton Fluence
(#/cm2)
1 year 2 years 3 years 4 years 5 years
1.19E+10
1.19E+10
1.19E+10
1.19E+10
1.19E+10
1.19E+10
1.18E+10
1.18E+10
1.18E+10
1.18E+10
1.18E+10
1.18E+10
1.17E+10
1.17E+10
1.16E+10
1.15E+10
1.14E+10
1.11E+10
1.08E+10
1.04E+10
9.83E+09
9.06E+09
8.05E+09
6.88E+09
5.65E+09
4.40E+09
3.24E+09
2.28E+09
1.49E+09
9.23E+08
5.48E+08
3.11E+08
1.61E+08
7.38E+07
2.20E+07
1.33E+10
1.33E+10
1.33E+10
1.33E+10
1.33E+10
1.33E+10
1.33E+10
1.33E+10
1.32E+10
1.32E+10
1.32E+10
1.32E+10
1.31E+10
1.31E+10
1.30E+10
1.29E+10
1.27E+10
1.24E+10
1.20E+10
1.16E+10
1.09E+10
1.00E+10
8.90E+09
7.57E+09
6.18E+09
4.77E+09
3.48E+09
2.42E+09
1.57E+09
9.67E+08
5.67E+08
3.23E+08
1.68E+08
7.68E+07
2.27E+07
2.06E+10
2.06E+10
2.06E+10
2.06E+10
2.06E+10
2.06E+10
2.06E+10
2.06E+10
2.06E+10
2.05E+10
2.05E+10
2.05E+10
2.04E+10
2.03E+10
2.02E+10
2.00E+10
1.97E+10
1.93E+10
1.87E+10
1.80E+10
1.70E+10
1.56E+10
1.39E+10
1.19E+10
9.73E+09
7.54E+09
5.51E+09
3.85E+09
2.50E+09
1.55E+09
9.10E+08
5.17E+08
2.67E+08
1.23E+08
3.66E+07
2.79E+10
2.79E+10
2.79E+10
2.79E+10
2.79E+10
2.79E+10
2.79E+10
2.79E+10
2.79E+10
2.79E+10
2.78E+10
2.78E+10
2.77E+10
2.76E+10
2.74E+10
2.71E+10
2.68E+10
2.62E+10
2.54E+10
2.45E+10
2.31E+10
2.13E+10
1.90E+10
1.62E+10
1.33E+10
1.03E+10
7.61E+09
5.34E+09
3.48E+09
2.16E+09
1.27E+09
7.23E+08
3.76E+08
1.72E+08
5.10E+07
3.51E+10
3.51E+10
3.51E+10
3.51E+10
3.51E+10
3.51E+10
3.51E+10
3.51E+10
3.51E+10
3.50E+10
3.50E+10
3.49E+10
3.48E+10
3.47E+10
3.45E+10
3.41E+10
3.37E+10
3.30E+10
3.20E+10
3.09E+10
2.92E+10
2.69E+10
2.40E+10
2.05E+10
1.69E+10
1.31E+10
9.75E+09
6.84E+09
4.47E+09
2.78E+09
1.64E+09
9.32E+08
4.83E+08
2.21E+08
6.52E+07
Values Do Not Include Design Margins
Table A-6. Integral Solar Proton Fluence Levels Behind Solid Sphere Aluminum Shields
100 mils (2.54 mm) Aluminum Shielding
A-6
CHECK WITH RLEP DATABASE AT:
http://vsde.gsfc.nasa.gov/index.jsp
TO VERIFY THAT THIS IS THE CORRECT VERSION PRIOR TO USE.
Radiation Environment for the LRO
Aluminum Shield
Thickness
g/sqcm mm
mils
0.007
0.03
1.02
0.021
0.08
3.06
0.027
0.10
3.94
0.041
0.15
5.98
0.048
0.18
7.00
0.062
0.23
9.04
0.069
0.26
10.06
0.082
0.30
11.96
0.089
0.33
12.98
0.103
0.38
15.02
0.199
0.74
29.02
0.302
1.12
44.06
0.398
1.47
58.03
0.501
1.86
73.07
0.597
2.21
87.05
0.802
2.97 116.93
1.001
3.71 145.94
1.248
4.62 181.97
1.502
5.56 219.02
1.749
6.48 255.04
2.003
7.42 292.09
2.503
9.27 364.96
2.997 11.10 437.01
3.498 12.96 510.24
3.998 14.81 583.07
4.499 16.66 655.91
4.999 18.51 728.74
6.001 22.23 875.20
8.003 29.64 1166.93
9.999 37.03 1457.87
431-SPEC-000020
Revision DRAFT
1 year
320.00
146.00
118.00
81.40
70.60
57.60
50.40
44.40
40.20
34.50
18.40
11.70
8.73
6.56
5.49
3.87
2.94
2.23
1.74
1.41
1.17
0.88
0.68
0.54
0.45
0.37
0.31
0.23
0.15
0.10
Total Dose
(krad-Si)
2 years 3 years 4 years
436.00 604.00 763.00
185.00 260.00 328.00
148.00 209.00 264.00
102.00 145.00 184.00
87.70 126.00 160.00
71.20 103.00 131.00
62.10
89.90 115.00
54.50
78.90 101.00
49.20
71.40
92.20
42.00
61.20
79.30
21.90
32.50
42.70
13.80
20.80
27.50
10.20
15.50
20.60
7.59
11.60
15.50
6.32
9.73
13.00
4.38
6.75
9.12
3.29
5.09
6.92
2.49
3.87
5.27
1.94
3.04
4.12
1.56
2.45
3.32
1.29
2.03
2.76
0.96
1.51
2.07
0.73
1.16
1.59
0.58
0.91
1.26
0.48
0.76
1.04
0.40
0.63
0.87
0.33
0.53
0.73
0.25
0.39
0.55
0.16
0.25
0.35
0.10
0.17
0.23
5 years
916.00
390.00
315.00
220.00
191.00
157.00
138.00
122.00
112.00
96.10
52.00
33.90
25.60
19.30
16.20
11.40
8.68
6.63
5.24
4.22
3.48
2.64
2.03
1.61
1.34
1.12
0.93
0.70
0.45
0.30
Values Do Not Include Design Margins
Table A-7. Total Ionizing Dose at the Center of Aluminum Spheres Due to Solar Proton
Events
A-7
CHECK WITH RLEP DATABASE AT:
http://vsde.gsfc.nasa.gov/index.jsp
TO VERIFY THAT THIS IS THE CORRECT VERSION PRIOR TO USE.
Radiation Environment for the LRO
LET
MeV*cm/mg
431-SPEC-000020
Revision DRAFT
LET Fluence
LET
#/sqcm/day
MeV*sqcm/mg
Solar Minimum
1.00E-03
1.65E-03
1.69E-03
1.70E-03
1.72E-03
1.77E-03
1.81E-03
1.85E-03
1.91E-03
1.98E-03
2.01E-03
2.13E-03
2.28E-03
2.53E-03
3.01E-03
3.54E-03
4.52E-03
5.56E-03
6.54E-03
7.52E-03
8.55E-03
9.60E-03
1.97E-02
2.96E-02
4.00E-02
5.04E-02
6.00E-02
6.97E-02
8.01E-02
9.00E-02
1.01E-01
2.00E-01
4.02E-01
LET Fluence
#/sqcm/day
Solar Maximum
4.25E+05
1.00E-03
4.24E+05
1.65E-03
3.29E+05
1.69E-03
3.04E+05
1.70E-03
2.84E+05
1.72E-03
2.54E+05
1.77E-03
2.30E+05
1.81E-03
2.12E+05
1.85E-03
1.90E+05
1.91E-03
1.72E+05
1.98E-03
1.67E+05
2.01E-03
1.46E+05
2.13E-03
1.27E+05
2.28E-03
1.07E+05
2.53E-03
8.29E+04
3.01E-03
6.87E+04
3.54E-03
5.55E+04
4.52E-03
4.90E+04
5.56E-03
4.58E+04
6.54E-03
2.76E+04
7.52E-03
2.13E+04
8.55E-03
1.75E+04
9.60E-03
7.02E+03
1.97E-02
5.07E+03
2.96E-02
4.33E+03
4.00E-02
3.81E+03
5.04E-02
3.50E+03
6.00E-02
2.91E+03
6.97E-02
2.66E+03
8.01E-02
2.40E+03
9.00E-02
2.23E+03
1.01E-01
9.84E+02
2.00E-01
4.33E+02
4.02E-01
Values Do Not Include Design Margins
1.54E+05
1.54E+05
1.07E+05
9.42E+04
8.46E+04
7.02E+04
5.98E+04
5.20E+04
4.34E+04
3.75E+04
3.59E+04
3.05E+04
2.69E+04
2.39E+04
2.11E+04
1.98E+04
1.88E+04
1.83E+04
1.82E+04
7.46E+03
5.04E+03
3.97E+03
1.88E+03
1.63E+03
1.55E+03
1.43E+03
1.36E+03
1.08E+03
1.01E+03
9.12E+02
8.74E+02
3.59E+02
1.52E+02
100 mils Aluminum Shielding
Table A-8. Integral LET Spectrum for Interplanetary Galactic Cosmic Rays (Z=1-92)
A-8
CHECK WITH RLEP DATABASE AT:
http://vsde.gsfc.nasa.gov/index.jsp
TO VERIFY THAT THIS IS THE CORRECT VERSION PRIOR TO USE.
Radiation Environment for the LRO
431-SPEC-000020
Revision DRAFT
LET
LET Fluence
LET
LET Fluence
MeV*cm/mg
#/sqcm/day
MeV*sqcm/mg
#/sqcm/day
Solar Minimum
6.03E-01
7.96E-01
1.00E+00
2.01E+00
3.02E+00
3.99E+00
5.03E+00
5.99E+00
8.00E+00
1.01E+01
1.11E+01
1.20E+01
1.30E+01
1.40E+01
1.50E+01
1.60E+01
1.70E+01
1.80E+01
1.91E+01
2.00E+01
2.49E+01
3.00E+01
3.49E+01
4.01E+01
4.50E+01
5.00E+01
5.06E+01
5.55E+01
6.02E+01
6.53E+01
7.00E+01
7.50E+01
8.04E+01
8.52E+01
9.03E+01
9.57E+01
1.00E+02
1.01E+02
1.03E+02
Solar Maximum
2.90E+02
6.03E-01
2.23E+02
7.96E-01
1.79E+02
1.00E+00
3.39E+01
2.01E+00
1.43E+01
3.02E+00
7.76E+00
3.99E+00
4.59E+00
5.03E+00
3.07E+00
5.99E+00
1.55E+00
8.00E+00
9.00E-01
1.01E+01
7.17E-01
1.11E+01
5.76E-01
1.20E+01
4.67E-01
1.30E+01
3.85E-01
1.40E+01
3.16E-01
1.50E+01
2.61E-01
1.60E+01
2.20E-01
1.70E+01
1.85E-01
1.80E+01
1.54E-01
1.91E+01
1.30E-01
2.00E+01
4.45E-02
2.49E+01
6.27E-04
3.00E+01
6.86E-05
3.49E+01
4.18E-05
4.01E+01
2.83E-05
4.50E+01
2.00E-05
5.00E+01
1.92E-05
5.06E+01
1.34E-05
5.55E+01
9.38E-06
6.02E+01
6.32E-06
6.53E+01
4.40E-06
7.00E+01
2.83E-06
7.50E+01
1.65E-06
8.04E+01
7.71E-07
8.52E+01
1.94E-07
9.03E+01
2.88E-08
9.57E+01
1.19E-08
1.00E+02
5.27E-09
1.01E+02
2.54E-09
1.03E+02
Values Do Not Include Design Margins
1.10E+02
8.84E+01
7.22E+01
5.88E+00
2.03E+00
1.02E+00
5.81E-01
3.80E-01
1.90E-01
1.10E-01
8.75E-02
7.04E-02
5.71E-02
4.72E-02
3.88E-02
3.20E-02
2.71E-02
2.27E-02
1.89E-02
1.60E-02
5.50E-03
8.18E-05
1.06E-05
6.50E-06
4.42E-06
3.13E-06
3.00E-06
2.11E-06
1.49E-06
1.01E-06
7.01E-07
4.52E-07
2.63E-07
1.23E-07
3.10E-08
4.60E-09
1.89E-09
8.41E-10
4.05E-10
Table A-8 (Continued)
A-9
CHECK WITH RLEP DATABASE AT:
http://vsde.gsfc.nasa.gov/index.jsp
TO VERIFY THAT THIS IS THE CORRECT VERSION PRIOR TO USE.
Radiation Environment for the LRO
431-SPEC-000020
Revision DRAFT
LET
LET Fluence
LET Fluence
LET Fluence
MeV*cm2/mg
#/cm2/s
#/cm2/s
#/cm2/s
Average Over Peak
Average Over Worst Day
Average Over Worst Week
1.00E-03
2.01E-03
3.01E-03
4.02E-03
5.01E-03
6.03E-03
7.02E-03
7.97E-03
8.95E-03
1.01E-02
1.99E-02
2.99E-02
4.00E-02
4.98E-02
6.00E-02
6.97E-02
8.01E-02
9.00E-02
9.99E-02
2.00E-01
3.01E-01
4.02E-01
5.01E-01
6.03E-01
7.01E-01
8.05E-01
9.04E-01
1.00E+00
2.01E+00
3.02E+00
3.99E+00
5.03E+00
6.06E+00
7.04E+00
8.00E+00
8.99E+00
1.01E+01
2.00E+01
2.52E+01
1.93E+05
5.21E+04
1.93E+05
5.21E+04
1.93E+05
5.20E+04
1.92E+05
5.17E+04
1.90E+05
5.11E+04
1.86E+05
5.02E+04
1.82E+05
4.90E+04
1.77E+05
4.76E+04
1.71E+05
4.60E+04
1.64E+05
4.40E+04
9.60E+04
2.55E+04
5.39E+04
1.43E+04
3.23E+04
8.56E+03
2.11E+04
5.59E+03
1.45E+04
3.84E+03
1.06E+04
2.81E+03
7.91E+03
2.09E+03
6.16E+03
1.63E+03
4.90E+03
1.29E+03
9.50E+02
2.51E+02
3.15E+02
8.31E+01
1.25E+02
3.32E+01
3.82E+01
1.01E+01
1.86E+01
4.94E+00
1.35E+01
3.58E+00
9.85E+00
2.62E+00
7.55E+00
2.02E+00
5.88E+00
1.57E+00
7.49E-01
2.06E-01
4.11E-01
1.13E-01
2.64E-01
7.29E-02
1.74E-01
4.80E-02
1.21E-01
3.36E-02
8.68E-02
2.40E-02
6.39E-02
1.77E-02
5.04E-02
1.40E-02
3.85E-02
1.07E-02
5.75E-03
1.60E-03
2.14E-03
5.95E-04
Values Do Not Include Design Margins
100 mils Aluminum Shielding
1.15E+04
1.15E+04
1.14E+04
1.13E+04
1.11E+04
1.08E+04
1.05E+04
1.01E+04
9.68E+03
9.19E+03
5.07E+03
2.78E+03
1.65E+03
1.07E+03
7.33E+02
5.34E+02
3.96E+02
3.08E+02
2.44E+02
4.67E+01
1.53E+01
6.08E+00
1.80E+00
8.78E-01
6.52E-01
4.91E-01
3.87E-01
3.10E-01
5.99E-02
3.33E-02
2.14E-02
1.42E-02
9.92E-03
7.11E-03
5.26E-03
4.13E-03
3.15E-03
4.63E-04
1.72E-04
Table A-9. Integral LET Spectrum for the October 1989 Solar Particle Event (Z=1-92)
A-10
CHECK WITH RLEP DATABASE AT:
http://vsde.gsfc.nasa.gov/index.jsp
TO VERIFY THAT THIS IS THE CORRECT VERSION PRIOR TO USE.
Radiation Environment for the LRO
431-SPEC-000020
Revision DRAFT
LET
LET Fluence
LET Fluence
LET Fluence
MeV*cm2/mg
#/cm2/s
#/cm2/s
#/cm2/s
Average Over Peak
Average Over Worst Day
Average Over Worst Week
3.00E+01
3.53E+01
4.01E+01
4.50E+01
5.00E+01
5.55E+01
6.02E+01
6.53E+01
7.00E+01
7.50E+01
8.04E+01
8.52E+01
9.03E+01
9.46E+01
1.00E+02
1.01E+02
1.03E+02
1.83E-05
5.10E-06
7.23E-07
2.01E-07
3.26E-07
9.08E-08
1.95E-07
5.44E-08
1.36E-07
3.78E-08
8.43E-08
2.35E-08
4.92E-08
1.37E-08
3.28E-08
9.12E-09
2.49E-08
6.92E-09
1.80E-08
5.00E-09
1.20E-08
3.34E-09
6.69E-09
1.86E-09
2.03E-09
5.64E-10
1.33E-10
3.71E-11
5.01E-11
1.39E-11
2.22E-11
6.19E-12
1.07E-11
2.99E-12
Values Do Not Include Design Margins
100 mils Aluminum Shielding
1.55E-06
7.14E-08
3.43E-08
2.12E-08
1.48E-08
9.31E-09
5.58E-09
3.75E-09
2.84E-09
2.04E-09
1.36E-09
7.56E-10
2.29E-10
1.51E-11
5.66E-12
2.51E-12
1.21E-12
Table A-9. (Continued)
A-11
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Energy
Proton Flux
Proton Flux
Proton Flux
MeV
#/cm2/s
#/cm2/s
#/cm2/s
Average Over Peak
Average Over Worst Day
Average Over Worst Week
1.00
1.75E+03
4.62E+02
8.85E+01
2.00
2.68E+03
7.09E+02
1.36E+02
3.02
3.47E+03
9.17E+02
1.76E+02
4.04
4.11E+03
1.09E+03
2.09E+02
5.04
4.62E+03
1.22E+03
2.36E+02
6.03
5.03E+03
1.33E+03
2.58E+02
7.02
5.33E+03
1.41E+03
2.75E+02
8.06
5.56E+03
1.47E+03
2.88E+02
9.00
5.69E+03
1.51E+03
2.96E+02
10.05
5.76E+03
1.53E+03
3.01E+02
14.99
5.41E+03
1.44E+03
2.92E+02
20.03
4.50E+03
1.21E+03
2.52E+02
24.98
3.57E+03
9.65E+02
2.07E+02
30.31
2.73E+03
7.40E+02
1.64E+02
35.27
2.11E+03
5.75E+02
1.31E+02
40.49
1.61E+03
4.42E+02
1.04E+02
50.50
9.91E+02
2.73E+02
6.79E+01
60.43
6.33E+02
1.75E+02
4.58E+01
70.33
4.20E+02
1.17E+02
3.20E+01
79.63
2.94E+02
8.18E+01
2.33E+01
90.17
2.03E+02
5.65E+01
1.68E+01
100.69
1.44E+02
4.01E+01
1.24E+01
150.25
3.84E+01
1.06E+01
3.80E+00
200.77
1.39E+01
3.79E+00
1.50E+00
299.59
3.32E+00
8.62E-01
3.88E-01
400.31
1.16E+00
2.85E-01
1.39E-01
499.23
4.97E-01
1.16E-01
5.96E-02
605.64
2.07E-01
4.64E-02
2.54E-02
704.94
1.10E-01
2.48E-02
1.44E-02
798.17
6.61E-02
1.48E-02
9.03E-03
903.74
3.95E-02
8.88E-03
5.66E-03
995.41
2.65E-02
5.96E-03
3.94E-03
Values Do Not Include Design Margins
100 mils Aluminum Shielding, CREME96
Note: Spectra were cut off at E =1 MeV and E=1000 MeV
Table A-10 Differential Proton Fluxes for the October 1989 Solar Particle Event
A-12
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Appendix B. Abbreviations and Acronyms
Abbreviation/
Acronym
DEFINITION
A-13
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A-14
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